The present invention is directed to a gaseous fuel burner system and method for process heating. More particularly, the present invention is directed to a burner system and method of operating the burner for reducing nitrogen oxides (NOx) emissions.
Energy intensive industries are facing increased challenges in meeting NOx emissions compliance. Natural gas is commonly used as a fuel due to its clean combustion and low overall emissions. Industrial burner manufacturers have improved burner equipment design to produce very low NOx emissions and call them by the generic name of “Low NOx Burners” (LNBs) or various trade names. LNBs are used in various industries including public utilities, incineration, refineries, chemical process, power generation, paper, food, rubber, etc.
Nitrogen oxides are among the primary air pollutants emitted from combustion processes. NOx emissions have been identified as contributing to the degradation of the environment, particularly degradation of air quality, formation of smog (poor visibility) and acid rain. As a result, air quality standards are being imposed by various governmental agencies, which limit the amount of NOx gases that may be emitted into the atmosphere.
Some low NOx burners used in these industries utilize fuel staging as a means to reduce NOx. By gradually adding fuel to the flame, the flame temperature may be kept lower, thereby limiting NOx formation. Many of these low NOx burners that have fuel staging lances also have a flame stabilizer. The flame stabilizer ensures that the main flame does not extinguish. The introduction of fuel and oxidant into a furnace without stable combustion can lead to serious safety issues.
Such burners with flame stabilizers and fuel staging lances have been designed to provide a fixed proportion of fuel to the flame stabilizer and fuel staging lances via suitable orifices. The orifices are sized to provide a proportional amount of fuel suitable over the range of use, including startup and production rate changes. The relative fuel split between the flame stabilizer and the fuel staging lances in the prior art burners is fixed.